In prior art systems passive RFID transponders have included a receiving antenna and a transmitting antenna. The need for separate antennae adds to the cost and complexity of the transponder. To address this limitation a number of single antenna transponders have been developed. That is, the transponder's antenna is used to both receive signals and transmit signals. Generally, these antennae are tuned to the received or interrogating frequency and, as such, the transmitted frequency can not differ greatly from the received frequency otherwise the antennae will not broadcast the transmitted signal efficiently. To transmit data at a high speed a low efficiency low Q antenna is required, however, to receive signals with high efficiency a high Q antenna is required.
This contradiction precludes the use of a high efficiency antenna for high speed data transmission. The transmission efficiency of all these systems is degraded by this tuning arrangement and otherwise compromised by the stray capacitance of the antenna coil.
In addition to this problem LC filter arrangements cannot be readily incorporated into ASIC systems and present several difficulties. It would accordingly be advantageous if alternate arrangements could be provided.
Furthermore, in passive transponders the electrical inertia of the power storage system limits the data rate. Examples of such known systems are disclosed in AU 55902/86, U.S. Pat. No. 4,546,241, U.S. Pat. No. 4,517,563, U.S. Pat. No. 4,075,632, U.S. Pat. No. 4,038,653, U.S. Pat. No. 3,832,530 and U.S. Pat. No. 3,299,424.